In a process of manufacturing a semiconductor wafer, chemical liquids such as photoresist liquid, pure water and organic solvent are used, and these chemical liquids are applied to the semiconductor wafer. For example, when the photoresist liquid is applied to the semiconductor wafer, this chemical liquid in a chemical liquid container is suctioned by a pump, and discharged from a discharge nozzle. As a mode of pump for discharging the chemical liquid, there are a mode in which a resin-made tube expanding and contracting in a radial direction is used as a pump member and a pump chamber is formed in this tube as described in JP H10-61558, and a mode in which a resin-made bellows expanding and contracting in an axial direction is used as a pump member and a pump chamber is formed between the bellows and a case accommodating the bellows as described in JP 2002-113406. Furthermore, as a mode of pump, there is a mode in which a diaphragm is used as a pump member.
In this chemical liquid supply device, the chemical liquid is filtered by a filter to remove particles and air bubbles contained in the chemical liquid.
As a mode of arrangement of filter, there are a mode in which it is placed on a primary side of the pump, and a mode in which it is placed on a secondary side of the pomp as described in JP 2002-113406. In the mode where the filter is placed on the secondary side of the pump, the filter is placed between the pump and the discharge nozzle, and the chemical liquid is filtered by supplying the chemical liquid to the filter with discharge operation of the pump. On the other hand, in the mode where the filter placed on the primary side of the pump, the filter is placed between the chemical liquid container and the pump, and the chemical liquid is suctioned and supplied to the filter with suction operation of the pump for filtering.
In the mode of placing the filter on the secondary side of the pump, it is possible to reliably filter the chemical liquid. However, since the discharge operation and filtering operation are simultaneously performed, the discharge amount is varied due to flow resistance of the filter. In this way, when clogging occurs in the filter or air bubbles are accumulated in the filter, the flow resistance of the filter is increased, as a result, a discharge pressure of the pump is increased and the discharge amount is decreased simultaneously, so it is impossible to continuously discharge the chemical liquid from the discharge nozzle with the same accuracy for a long period of time. As such, when the flow rate and the discharge amount of the chemical liquid is changed due to a secondary factor in the filter, original discharge capabilities of the pump cannot be achieved in this mode.
On the other hand, in the mode of placing the filter on the primary side of the pump, since the filter is not placed on the secondary side of the pump, an influence of the clogged filter on the discharge accuracy is small. However, when the chemical liquid passes through the filter with the suction operation, the chemical liquid is placed in a negative pressure state, and bubbles generated from gas dissolved in the chemical liquid are mixed in the chemical liquid. As a result, a circuit pattern on a semiconductor wafer tends to have a defect, thereby increasing faulty products. In order to improve this situation, it is necessary to provide a system for removing air bubbles to the chemical liquid supply device, and it is inevitable that this device is complicated in configuration and increased in production cost.
As described in JP 3286687 and JP 2007117787, it is known that, in order to solve these problems, a filter is placed between two pumps in a chemical liquid supply device, the chemical liquid is supplied by a first pump from the chemical liquid container to the filter, and the filtered chemical liquid is passed into a second pump by suction.
However, if two pumps are provided to one chemical liquid supply line, the device becomes not only expensive and large in size, but also complex in pipe arrangement, control programs and the like. Furthermore, if a buffer tank is used between the filter and the second pump as described in JP 2007117787, since the surface of the chemical liquid accommodated in the buffer tank comes in contact with air, the chemical liquid contacted by air turns into a gel, and particles are mixed in the chemical liquid.